Synthesis and physico-chemical properties of semiconducting ZnCr₂Se₄-policrystals doped with dysprosium

The compound ZnCr₂Se₄ crystallizes in cubic spinel structure and is a semiconductor with helical magnetic structure below the Néel temperature T_N = 20 K with a strong ferromagnetic (FM) component confirmed by a large positive Curie-Weiss temperature (q) of 115 K. It is known that elements substitution can strongly influence on parent compound properties. In our research we used dysprosium as a dopant.

The compounds based on the system Zn_1-xDy_x­Cr₂Se₄ were synthesized by ceramic method, according to the following reactions: 

(1 − x)ZnSe + xDySe + Cr₂Se₃ = Zn_1−xDy_x­Cr₂Se₄, x = 0.05÷0.1 

ZnSe + (1 − x)Cr₂Se₃ + xDy₂Se₃ = ZnCr_2−xDy_xSe₄, x = 0.05÷0.1

XRD and Rietveld refinement analysis were used in order to obtain structural parameters. Chemical composition defined using JEOL scanning microscope (SE 6480). The results showed less Dy content then it was expected. The structural parameters increase with increasing of Dy amount. The results of XRD analysis showed only one spinel phase.

Fig.1 The polycrystalline compounds obtained in the ZnCr₂Se₄:Dy system: Zn_0.98Cr_1.68Dy_0.06Se₄ (left side), Zn_0.92Dy_0.06Cr_2.01Se₄ (right side) 

The magnetic isotherms of the obtained compounds were studied using high magnetic stationary fields (up to 14T). It was confirmed increasing of magnetization with increasing of Dy ions, in tetrahedral and octahedral positions, respectively.

Decreasing of paramagnetic Curie-Wiess temperature with increasing of Dy amount indicates the boost of the antiferromagnetic interactions.

The results of XANES and EXAFS showed that Dy³⁺ ions are located in the same chemical environment.